The continuing miniaturization of electronic devices has led to a variety of portable audio devices that deliver audio to a listener via headphones. The miniaturization of electronics has also led to smaller and smaller headphones that produce high quality sound. Some headphones now include noise cancellation systems that include microphones for obtaining external sound data and a controller for reducing or cancelling the external sounds that are generated in the user's environment.
Ear canal shapes, angles and sizes vary greatly among different persons. Many users feel uncomfortable to wear conventional in-ear headphones despite of different ear tips that come with the headphone products. Air seal, which is essential for good low frequency extension, is poor in many cases. Also, in-ear headphones tend to loosen or even fall off. Around-the-ear headphones are usually heavy, bulky and unsuitable for portable applications. On-ear headphones suffer from poor air seal, which limits their low-frequency performance and overall audio quality.